Cytomegalovirus CMV

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Cytomegalovirus (CMV) is a member of the Herpesvirus family and is also known as Human Herpes Virus 5 (HHV-5).

  • Infection is usually symptom-free and over 50% of adults have serological evidence of latent infection.
  • Immunocompromised patients can have sight- or life-threatening disease.
  • Prevalence is global


The most important effect is as an opportunistic infection in the immunocompromised


See also these assocated articles:


Aetiology

  • Prevalence = up to 50% of adults have latent infection
  • Age: 1% annual seroconversion rate.
    • Toddlers at playschool and adolescents have a much higher conversion rate.


Infection is spread via exchange of bodily fluids:

  • Kissing
  • sexual intercourse
  • transfusions
  • vertical transmission in-utero
    • Congenital CMV infection may have serious consequences for the foetus.


Clinical features

In Healthy adults, infection is usually asymptomatic, though may produce an illness similar to Infectious Mononucleosis:

  • fever
  • lymphocytosis with atypical lymphocytes
  • hepatitis


In immunocompromised patients, disseminated fatal infection may occur, including:

  • encephalitis
  • retinitis
  • pneumonitis


Intra-uterine infection (Congenital CMV infection) usually occurs during primary infection of the mother. Consequences include:

  • CNS: microcephaly and motor impairment
    • Peri-ventricular calcification may be seen on Xray imaging.
  • Hepatosplenomegaly, jaundice
  • Thrombocytopenia
  • Haemolytic anaemia


Investigations

Serological Testing

  • Latent Infection - IgG positive, IgM negative
  • Primary Infection - IgM positive


Histology

  • Cytomegalic inclusions cell (from which the virus derives its name):
    • Enlarged cells
    • Classical Owl's Eye inranuclear inclusions on staining.


Immunofluorescence allows identification of antigen in culture.


Polymerase Chain Reaction - PCR can provide a sensitive and quantitative assay of CMV in body fluids / blood.


The Paul Bunnell Test for heterophile antibodies will be negative.


A blood film may show atypical lymphocytosis.


Management

Infection in immunocompetent patients is usually self-limiting and requires no treatment.


Primary infection in a pregnant mother requires careful assessment and follow-up. Effects on the foetus may be dependence on gestation.


Immunosuppressed patients

Ganciclovir reduces retinitis, GI damage and can eliminate the virus from bodily secretions and blood. It is less effective against pneumonitis.

  • Maintenance therapy may be necessary where immunosuppression is not transient eg. HIV and transplant patients.
  • Drug resistance has been reported
  • Bone marrow toxicity does occur
  • Toxicity may prevent use in neonates.


Foscarnet and Cidofovir are also used to treat CMV infection

  • Both are nephrotoxic
  • Use is restricted to severe disease


References

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